Hitherto, adsorptive particles such as zeolite, silica gel, activated carbon and mesoporous silica have been extensively used in various applications such as separation and purification of various gases, filters, adsorption heat pumps, catalysts, humidity control and deodorization. The adsorptive particles have been coated or supported together with a binder on an adequate base material and have been used in various configurations such as plates, tubes, honeycombs, sheets, nets and nonwoven fabrics.
For example, adsorptive heat pumps and desiccant systems are systems for heat transfer and humidity control using adsorption and desorption functions of adsorptive materials, and can be applied to various apparatuses utilizing a low-temperature exhaust heat from cogeneration systems such as cooling devices, heating and cooling apparatuses and humidity controllers. In the apparatuses using the adsorptive heat pumps, warm heat is produced by heat of adsorption in the module including the adsorptive material, whereas cold heat is produced by latent heat of vaporization in the vaporization module. Also, in the apparatuses using the desiccant systems, dehumidification is conducted in high-humidity seasons, whereas humidification is conducted in low-humidity seasons. Any of the apparatuses is effective for construction of comfortable spaces.
In recent years, in order to improve a performance of an adsorptive member used in an adsorption device of the above adsorptive heat pumps and desiccant systems and in order to reduce a size of these apparatuses, there have been made studies on the technique of applying an adsorptive material onto a heat exchanger or a honeycomb rotor.
For example, as a member for a heat exchanger of adsorption-type freezers, there may be used an adsorptive member obtained by directly applying an adsorptive material onto fins of the heat exchanger. More specifically, there has been proposed an adsorptive member obtained by applying an adhesive acrylic binder onto a plurality of aluminum fins, and bonding a powdery silica gel having a mesh size f 20 to 35 (particle diameter: about 450 to 850 μm) onto a surface of the acrylic binder (Patent Document 1). Also, there has been proposed the use of adsorptive particles such as zeolite, silica and alumina together with an inorganic binder such as colloidal silica, water glass and aluminum phosphate (Patent Documents 2 to 4). In addition, there has been proposed the use of these inorganic binders in combination with thermoplastic resins or cellulose-based organic binders (Patent Documents 5 and 6).
In addition, there has been proposed the use of zeolite or silica gel in combination with a resin binder having a glass transition temperature (Tg) of not lower than 35° C. (Patent Documents 7 and 8). More specifically, there has been proposed an adsorptive sheet using, as a binder, a cured product obtained by curing a bisphenol A-type epoxy resin by adding a curing agent thereto, or an adsorptive sheet using, as a binder, a high-molecular weight bisphenol A-type phenoxy resin without adding any curing agent thereto. Further, there has been proposed an adsorptive sheet using these binders in combination with a vinyl acetate resin, etc., to improve an adhesion property thereof. These resin binders may be used in the form of an aqueous emulsion in which water and the binder resin are subjected to phase separation, and therefore the aqueous phase is eliminated upon drying after coating the slurry, so that flowing paths of gases are formed around the respective adsorptive particles. For this reason, the resulting material can be enhanced in both of adhesion property and adsorption performance, so that it is possible to obtain an adsorptive member which is more excellent than the above binder.
On the other hand, with respect to the rotor-shaped adsorptive member which can be applied to desiccant systems, there has been proposed the use of a polyvinyl alcohol binder together with Y-type zeolite (Patent Document 9).
Meanwhile, with the recent development of a variety of heat sources which can be used in adsorptive heat pumps and desiccant systems as well as with the recent reduction in the size of these apparatuses, it has also been required that the adsorptive member used therein meets strict performance requirements. In particular, in the application field of warm heat production in adsorptive heat pumps in which a high temperature exceeding 120° C. tends to be used, it has been required that binders used therein are strictly controlled in their properties such as thermal stability and adhesion strength. For these reasons, at present, conventionally known adsorptive members have failed to satisfy these performance requirements.
For example, the binders formed of a bisphenol A type epoxy resin are relatively thermally stable, but fail to fully suppress a stress against a base material due to temperature change. Therefore, there tends to occur such a problem that a coating film produced therefrom is peeled off when subjected to heat cycle. Also, the high-molecular weight phenoxy resin in an uncured state can exhibit a sufficient flexibility but tends to be insufficient in adhesion property, and the phenoxy resin cured by adding a curing agent thereto can be improved in adhesion property but tends to be poor in flexibility. As a result, in any cases, the coating film produced from the phenoxy resin tends to suffer from the defects. Further, when using the above resin in combination with a vinyl acetate emulsion, etc., there tends to occur such a problem that the resulting binder has a poor heat resistance and therefore suffers from thermal decomposition and generation of outgases owing to the thermal decomposition which tends to result in deterioration of a vacuum degree inside of heat pumps. Also, the binder formed of polyvinyl alcohol tends to have a poor heat resistance and therefore tends to suffer from such a problem that a desiccant rotor using the binder by itself is deteriorated in heat resistance.